Typically, a construction machine, such as a bulldozer or an excavator, designed to work on an uneven terrain includes an operation/control cab provided on a vehicle body frame to which a carriage is attached. As compared with a general vehicle, a large external force is transmitted to the cab from the vehicle body frame. In view of this, the cab is mounted on the vehicle body frame via an anti-vibration mount that functions as a vibration suppressor.
A so-called hydraulic mount has been known as an anti-vibration mount (see, for instance, Patent Literature 1).
FIG. 17 shows a hydraulic mount 90 disclosed in Patent Literature 1. The hydraulic mount 90 includes: a cup-shaped container 91; a cylindrical plate 92 provided to the upper opening of the container 91; a rubber mount 97 fixed to the cylindrical plate 92; a collar 98 fixed to the rubber mount 97; a rod 93 vertically penetrating through the collar 98; a damper plate 94 bolded to the lower end of the rod 93; and a spring 95 interposed between the lower surface of the damper plate 94 and the bottom of the container 91.
A high-viscosity fluid 96 such as silicone oil is sealed in the container 91. The interior of the container 91 is divided into a lower fluid chamber 911 defined at the lower side of the damper plate 94 and an upper fluid chamber 912 defined at the upper side of the damper plate 94.
The rubber mount 97 having elasticity is fixed to the cylindrical portion of the cylindrical plate 92. The cylindrical collar 98 vertically penetrates the rubber mount 97 and is bonded to the rubber mount 97 by vulcanizing adhesion or the like. A bearing 102 and a seal ring 99 are attached to the inner circumference of the collar 98, and the rod 93 penetrates through the bearing 102 and the seal ring 99 in a vertically slidable manner.
Above the upper fluid chamber 912, an air chamber 100 is provided by a depression formed in the lower surface of the rubber mount 97.
In the hydraulic mount 90, the respective flanges of the container 91 and the cylindrical plate 92 are fixed to a vehicle body frame (not shown) using a bolt while the upper end of the rod 93 is bolted to the lower surface of a cab (not shown). Thus, the cab is supported on the vehicle body frame via the spring 95.
Horizontal vibration of the cab relative to the vehicle body frame is absorbed and damped by elastic deformation of the rubber mount 97 caused when the rod 93 is pressed against the rubber mount 97. In contrast, vertical vibration of the cab relative to the vehicle body frame is absorbed mainly by elastic deformation of the spring 95 while being damped by fluid resistance resulting from the movement of the damper plate 94 in the high-viscosity fluid 96.
The damping effect on the vertical vibration will be described below in detail. When, for instance, the rod 93 is pressed into the container 91 in response to the vertical vibration of the cab, the downward movement of the damper plate 94 forces the high-viscosity fluid 96 in the lower fluid chamber 911 to flow into the upper fluid chamber 912 through a clearance 101 defined between the outer circumference of the damper plate 94 and the inner circumference of the container 91, and the resulting fluid resistance (shear resistance) generates a damping force.
When the rod 93 moves upward after being pressed, the high-viscosity fluid 96 reversely flows from the upper fluid chamber 912 into the lower fluid chamber 911.
An arrangement where an engine mounted on a vehicle is supported via a hydraulic mount has been frequently employed (see, for instance, Patent Literatures 2 and 3).
In a hydraulic mount disclosed in Patent Literature 2, an engine is supported by an elastic support plate in a vibration-proof manner. A fluid chamber is formed below the support plate and is divided into upper and lower parts by a partition plate with an orifice. The lower part of the fluid chamber is closed by an elastic thin plate.
When, for instance, the support plate is moved downward to be deformed in response to vertical vibration, the volume of the upper part of the fluid chamber is reduced, so that a fluid in the upper part of the fluid chamber flows into the lower part of the fluid chamber through the orifice. When the flowing fluid passes through the orifice, the resulting fluid resistance generates a damping force. The elastic thin plate covering the lower part of the fluid chamber is elastically deformed in accordance with the amount of the fluid flowing from the upper part to increase the volume of the lower part of the fluid chamber.
When the support plate returns upward, the volume of the upper part of the fluid is increased, so that the fluid reversely flows into the upper part from the lower part of the fluid chamber. The mechanism to generate the damping force uses the fluid resistance caused when the fluid passes through the orifice. The function of the orifice resistance according to Patent Literature 2 is substantially the same as that of the shear resistance caused by the damper plate according to Patent Literature 1.
In a hydraulic mount disclosed in Patent Literature 3, a damper plate is integrally provided to the lower surface of a support plate that is substantially the same as that of Patent Literature 2, and is housed in a fluid chamber. Thus, the fluid chamber is likewise divided into upper and lower parts by the damper plate. The bottom of the fluid chamber is closed by an elastic thin plate and is elastically deformed following a change in the volume of the fluid chamber resulting from the deformation of the support plate. This is basically the same as the technique of Patent Literature 2.
However, in Patent Literature 3, a mechanism to generate a damping force uses shear resistance resulting from the movement of the damper plate in the fluid chamber, which is substantially the same as in Patent Literature 1.
Incidentally, in the hydraulic mounts of Patent Literatures 2 and 3, a mounted object such as an engine is supported via a rubber support plate having a relatively large rigidity, so that when the mounted object stands still, the weight of the mounted object is supported as an initial vertical load via the support plate. Usage of these hydraulic mounts as the cab mount of a construction machine requires a further increase in the rigidity of the support plate. Specifically, since these hydraulic mounts have a small damping effect on horizontal vibration, the hydraulic mounts cannot prevent the horizontal vibration of the cab, which results in a poor ride quality. Suppression of this vibration requires an increase in the horizontal rigidity. However, such an increase leads to an increase in the vertical rigidity, so that anti-vibration effect is impaired. In order to avoid the increase in the vertical rigidity, there has been suggested a construction machine cab mount that uses, for instance, a rubber support plate to allow the suppression of the horizontal cab vibration and a reduction in the vertical rigidity (improvement in the anti-vibration effect) (e.g. Patent Literature 4).
In contrast, in the hydraulic mount of Patent Literature 1, the horizontal direction of the cab is supported by a rubber having a large rigidity while a vertical load is supported by the vehicle body frame via the relatively-soft spring 95, thereby reducing a vertical static spring constant. Thus, it is possible to prevent a bumpy feeling when a low frequency vibration is input, so that the ride quality is preferable.